The Master Builder

Greg Thomas absolutely loves carpentry. He once bought an apartment building near Aspen, Colo., and spent five years single-handedly renovating its 24 rundown units. Thomas did everything from hanging drywall to building counters to replacing plumbing.

Today, his handiwork involves providing dependable and growing retirement income for baby boomers. "I suppose you could say that I build income streams," says Thomas, who...